This dissertation focuses on the acquisition of stress in Greek L1. It
investigates phonological development in a language with a lexical accent
system, where the position of stress is determined by the
phonology-morphology interface. It demonstrates that the acquisition of
stress in lexical accent systems proceeds differently compared to languages
with less complex or non-lexical accentual systems.

The production of multiple truncated outputs of various prosodic shapes as
well as faithfully produced forms during the same phases of phonological
development lead to the conclusion that children employ multiple parallel
grammars generated by the permutation of universal and innate constraints,
and follow several developmental paths during the acquisition process. This
implies that language development does not proceed in a strictly stage-like
fashion fashion, as has often been previously assumed. I argue that
learning proceeds in three major phases. In the first phase, the child
grammar is in a state where all markedness constraints dominate all
faithfulness constraints. Then, during the second developmental phase
constraint permutation results in a radical expansion of grammars.
Constraint permutation provides a huge number of grammars. In language
acquisition, all possible rankings predict all possible developmental paths
children follow in their task of acquiring the phonology of their language.
In the third phase of their phonological development, Greek children are
considered to have reached the final state of the adult grammar.

Two interesting observations stem from the Greek child data: First, the
number of accessed grammars may decrease as learning proceeds, leading to
the use of only one grammar, i.e. the fully faithful adult grammar. More
specifically, if learning proceeds without regressive steps, grammars are
gradually filtered and left out from the multiple grammars' inventory up to
the point children reach the final state of the target grammar. However, if
regressions to earlier stages of development occur, then grammars may be
activated and deactivated in parallel during this second phase of
development. This is possible until positive evidence and frequency effects
of child-directed speech leads the child to the adoption of the 'correct'
final grammar. Both of these distinct developmental patterns characterize
the phonological development of Greek children.

Output variation further challenges the idea of the trochaic bias,
according to which there is a cross-linguistic preference for disyllabic
trochees in child speech. Additionally, the notion of 'stage' is not
completely abandoned but it is revised and redefined. Here, a stage is not
synonymous with a period of time in which children's productions are
relatively uniform. Rather, it refers to a phase in language acquisition, a
chronological slot, associated with a set of co-emerging grammars that
share specific characteristics.

The multiple parallel grammars model developed here refers to production
but also has important implications for perception, since it makes the
prediction that the latter may be characterized by multiple grammars as
well. It may also be relevant for the study of synchrony and diachrony,
given that it can provide a unified account of synchronic, diachronic and
language change phenomena.